US 5,686,866 A · Phase locked loop providing fast tuning for large frequency changes

Abstract

A more rapid charging of an integrating capacitor of a PLL is provided when large frequency changes are desired. In one embodiment, the phase locked loop (PLL) circuit sinks or sources current to charge or discharge the integrating capacitor. A threshold voltage proportional to a current through the capacitor turns on an augmenting circuit which sinks or sources more current of the proper polarity to the integrating capacitor from an external source until a PLL lock is achieved. Once the lock is achieved, if a small correction current is required by the PLL, the small correction current is below a threshold required to actuate the augmenting circuit, and the PLL loop behaves in the usual manner as if the augmenting circuit were not present. In another embodiment, the integrating capacitor is reduced in value by switchably connecting a second capacitor in series with the integrating capacitor so that the total reduced capacitance of reduced value can be charged more quickly.

Claims7

Dependent claims

A tuning system for a television apparatus, comprising:

a phase detection means of a PLL for providing a tuning signal for the tuning of the apparatus in response to a signal selection;
means for tuning a receiver comprising an integrating means;
means for coupling a version of the tuning signal to the integrating means for integrating the version of the tuning signal over a first response time, the integrating means comprising an integrating capacitor which is one of charged or discharged by current responsive to the tuning signal, and
means for augmenting the one of charging and discharging of the integrating capacitor responsive to the tuning signal for charging and discharging the integrating capacitor over a second response time which is faster than the first response time, said augmenting means comprising coupling an additional current from a power supply source to the integrating means in response to a parameter of the tuning signal,
the means for augmenting includes means responsive to the amplitude of the current of one of charging and discharging the integrating capacitor.

2 more elements

Dependencies are inferred from the claim text.

Phase locked loop providing fast tuning for large frequency changes

Life of this patent

Phase locked loop providing fast tuning for large frequency changes

Life of this patent

Abstract

Claims7